Some of this information, such as when the war started and its basic causes, comes from an historical archive screen in "In a Mirror, Darkly, Part II". The initial death toll matches the "despotic" deaths mentioned by Spock in "Bread and Circuses" as being from WWIII. See the Eugenics Wars for a discussion of Spock's comment on the "last so-called world war" from "Space Seed."

Colonel Green's activities during the war were often cited as "genocidal" and treacherous. He and his troops personally killed hundreds of thousands of individuals affected with radiation sickness and other "impurities," using as a rationale that it was necessary in order to prevent their passing on such traits to later generations. (ENT: "Demons", "Terra Prime") He was notorious into the 23rd century for striking at his enemies in the midst of negotiating with them. (TOS: "The Savage Curtain")

Despite an escalating and ongoing global conflict, manned space exploration continued into the early 2030s with at least one mission to Mars. (VOY: "One Small Step") The New United Nations was also founded during these early years of World War III, and was among the first attempts to rebuild humanity during this era; for instance, by 2036, it had declared that no Human being would be held accountable "for the crimes of their race or forebearers." But not everyone heeded or respected this decree and some parts of the world later "abolished all United Earth nonsense." (TNG: "Encounter at Farpoint")

Colonel Green in 2056

Humanity eventually turned over a new leaf when a few courageous people began to realize that they could make a difference. (ENT: "Judgment") The war culminated circa 2053, when several of Earth's governments met in San Francisco to declare a cease-fire, effectively ending the war. (ENT: "Demons") As a result of this world war, like the two before it, whole generations were nearly wiped out. (ENT: "Judgment") The use of nuclear weapons engulfed Earth with an immense dust cloud, resulting in numerous nuclear winters. (TNG: "A Matter of Time") When it was over, Earth's atmosphere was irradiated with a detectably heightened amount of radioactive isotopes. (Star Trek: First Contact)

Three years later, Colonel Green gave an impassioned speech asking for the impure to once again be purged from society. (ENT: "Demons")

A trial in an area heavily affected by World War III

In 2063, a short time after Earth emerged from this global war, First Contact was made with the Vulcans, leading to increased recovery from the war for parts of the world. (Star Trek: First Contact) When news of this event reached Vulcan, some Vulcans, including V'Lar, were fascinated by humanity, but also worried, believing the idea that Humans had deemed themselves ready to join the interstellar community, so soon after the war, seemed premature. (ENT: "Fallen Hero") Indeed, for several years after first contact, various parts of Earth were still affected by what became known as the "post-atomic horror." In 2079, one such culture reverted to a state of near-barbarism that followed the credo "Kill all the lawyers," and "Guilty until proven innocent." (TNG: "Encounter at Farpoint") Due to these and other factors, parts of Earth continued to be in – as Captain Jean-Luc Picard put it in 2365 – "chaos" well into the early 22nd century. (TNG: "Up The Long Ladder")

By the early 2100s – less than two generations of the post-atomic horror – humanity was finally able to eliminate most if not all poverty, disease, war and hunger. Along with it, a lot of other things disappeared from humanity, including hopelessness, despair, and cruelty. (TNG: "Time's Arrow, Part II"; Star Trek: First Contact; ENT: "Broken Bow")

The legacy of the war was felt in many ways during the hundred years after its conclusion. It was the subject of many films during that time and, in 2153, one of these epics won a majority of movie awards. (ENT: "Home") In the early 22nd century, the philosophy of Neo-Transcendentalism was founded by Liam Dieghan; he advocated "a return to a simpler life" in response to the war's carnage. (TNG: "Up The Long Ladder") The war additionally influenced the powerful xenophobic movement of mid-22nd century Earth known as Terra Prime. Led by John Frederick Paxton, the organization drew inspiration from the war through adoption of Colonel Green's goals and teachings concerning a "pure" Human race. It also blamed the Vulcans for not stopping the war with their superior technology, and thereby saving the lives of hundreds of millions of people. This blame was then channeled into a general distrust of all non-Humans. (ENT: "Demons", "Terra Prime")

Like the Earth-Romulan War, very few details have been presented in Star Trek on World War III. In 1996, this event received a Trekker's Choice Award for the 'Oft Heard but Never Seen' Award, as being "the favorite historical moment only alluded to in Star Trek."

According to the 40 Years of Star Trek: The Collection auction catalog, during the middle of ENT Season 4, plans were in place for an episode to feature Colonel Green. It was planned to link Q's World War III uniform to the Colonel by having the emblem on Q's hood appear on flags representing Green. Such a flag was created for "In a Mirror, Darkly", and seen in the briefing room aboard the ISS Enterprise. When Enterprise was canceled, plans for the episode fell through and all that remains of the link between Q's uniform and Colonel Green is the flag seen in the mirror universe.